Safety markings are understood to be markings on goods and products or their packaging, which cannot be forged or, at the very least, are very difficult to copy, and the absence of which is intended to disclose unauthorized imitations or copies (forgeries). These include watermarks, logos, serial numbers, special inks or hologram images.
However, the known safety markings do not offer adequate protection against imitations or are expensive to produce or cannot be used everywhere. Moreover, when previously customary markings are used, the checking of the authenticity is complicated and expensive. Either test pieces have to be investigated or laboratory tests to analyze the material or image must be carried out. Frequently, the results are not reliable.
The production of safety markings on the packaging of goods or on the goods themselves by the CIT principle (“Concealed Image Technologies”) is suitable for checking the genuineness of a product in situ easily and quickly. The safety markings are two-dimensional or three-dimensional images, which because of the small size and the arrangement of the image elements, are not visible to the human cyc (“hidden images”) in printed areas. These hidden images can be reproduced only at great expense, if at all, since scanners cannot detect the coded image information because of the small size (less than 50 μm), the variable point or line frequency and the variable alignment. An optical encoder (lens), which matches only the respective hidden image according to the key-lock principle, is required to make such markings visible. The 3D CIT technology employs 1-30 μm wide and 1-50 μm deep depressions, which are embossed or produced by laser technology and code image information due to their different reflection angles. The WO 2004/096570 A2 discloses a method for producing embossed 3D hidden images. The image information is disposed at lines with a frequency of 1000 L/inch with a particular alignment. However, 3D CIT can be used only with plastic film or metal foil and is therefore limited. 2D CIT images can be produced with different printing methods such as offset printing, gravure printing or flexographic printing. The preliminary image files, created for printing product packaging, for example, are manipulated pixelwise or linewise by specialized companies, so that the image information for the CIT safety marking remains hidden to the eye. Slight chrominance or shade differences from the surrounding area arc used for coding purposes. It is a disadvantage of the known 2D CIT methods that they can be employed only within rastered image data. In full tone areas, which are of great importance for the printing of packaging material, it has, until now, not been possible to implement the hidden image method.
It is therefore an object of the invention to create a printable safety marking according to the CIT principle which can be implemented at little expense at any place of a material being printed and therefore also in areas that are not rastered.